Michell clamp too tight for Spacedeck?

Why would anyone use clamp?
I read that audiophiles experiment with different mats in hopes of decoupling a record form the platter and dampening the resonance/ vibration in the record.

when I bought the Funk Achromat, I found I preferred the sound without a clamp. It's also less hassle. So I no longer use my clamp - and actually sold them.

do you mean the collet won't fit easily on the spindle? I have 2 of these clamp and the older one fits loose, the new one initially fit very tight. I had to mash it onto the spindle with moderate force. It loosened up with a little use though. I believe if you remove the collet from the clamp you may be able to hasten the "loosening".

Are you suggesting that I remove the collet from the clamp and just leave it on the spindle for prolonged periods of time to "enlarge" the collet?

yes, I would do this for an overnight, and maybe place/remove it a few times by itself (ie not inserted in the clamp). If that doesn't loosen it up, I'd find something slightly larger than the spindle (a bolt, or screwdriver, etc)to enlarge it slightly.